The present invention relates to an apparatus for automatically transporting sheets of original. More specifically, the invention relates to an apparatus for automatically transporting sheets of original from an original stacking part, in which the sheets of original are stacked, to a position in an image forming apparatus for reading information from the original.
A copying machine, for example, may have an automatic document feeder (referred to as ADF below) on its upper surface. The ADF has a tray for original in which sheets of original are stacked, an original transporting system, and an original discharging part. In the ADF, the sheets of original in the original tray are transported one by one by the original transporting system to a contact glass in the copying machine. Then, the image information from the original is read by a reading system in the copying machine. After the image information is read, the sheet is discharged to the original discharging part by the original transporting system.
Original transporting systems of ADFs such as the above ADF usually consist of a belt mechanism, and a roller mechanism to drive the belt, as disclosed in U.S. Pat. No. 4,589,650 and Japanese Patent Laying-Open No. 201644/1988. An apparatus according to the disclosure in the above documents must be large and have complex structure. Consequently, not only automatically feeding sheets of original, but also, manually setting a stack of original, such as a book, are difficult for an operator using the conventional ADF of a small or a mid-size type of machine.
U.S. Pat. No. 4,632,376 discloses an apparatus which comprises an original transporting system and which includes a simple structure comprised of a plurality of rollers, instead of a belt mechanism. However, the apparatus is unwieldy, since the original stacking part and the original discharging part are disposed above the contact glass. Therefore, it is difficult for an operator to open or close the apparatus manually. Furthermore, the apparatus has a U-shaped path for feeding sheets of original, whereby the sheets occasionally are not set in the proper position on the contact glass, but out of the proper position.
To solve the above problems, the commonly assigned, copending U.S. patent application Ser. No. 07/322,914, discloses an ADF comprising an original transporting system of simple mechanism, suitable for small-size and mid-size copying machines. This ADF can be opened and closed easily, and seldom causes improper positioning of original sheets (the Japanese counterpart application was published as Japanese Patent Laying-Open No. 236126/1989 on Sept. 21, 1989, later than the priority date of this application).
FIG. 1 shows a part of the original transporting system of the above application. The original transporting system includes a transporting roller 2 which presses against a contact glass 1. Sheets of original are transported from an original stacking part 3 located beside the contact glass 1 through a discharge guide 4 to the nipping position between the contact glass 1 and the transporting roller 2. Then, the sheet of original is nipped between the transporting roller 2 and the contact glass 1 in order to correct its position in the transportation, and it is transported by the transporting roller 2 to the right in FIG. 1, until the sheet is located in a predetermined position on the contact glass 1. Thus, the transporting roller 2 functions herein not only for transporting the sheet, but also for resisting the sheet, in order to correct the sheet position. After the information from the sheet of the original is read by the original reading apparatus of the copying machine, the transporting roller 2 starts rotating in the opposite direction, shown by the dotted arrow in FIG. 1, so that the sheet of original is scooped by the discharging guide 4 and then discharged to the original discharging part located above the contact glass 1.
However, guiding an edge of an original sheet to the nipping position is sometimes difficult in a transportation system comprising the contact glass 1 and the transporting roller 2 which presses thereon, by comparison to a transportation system comprising a pair of rollers which press on each other, or a transportation system including a belt. Particularly, in the transportation system shown in FIG. 1, the outer surface of transporting roller 2 must be made of a friction material, such as resin, due to the fact that it must perform a plurality of functions--as a resist roller, a supplying roller, and a discharging roller--on the contact glass. Accordingly, it is sometimes difficult to guide the leading edge of a sheet of original into the nipping position, after the edge of the sheet has moved onto the surface of the transporting roller 2. It can easily happen that the edge of a thin sheet of original becomes curled, causing defective transportation.